The invention relates to acoustical silencers, including vent silencers. The invention arose during continuing development efforts related to the vent silencer shown in Hall et al U.S. Pat. No. 4,108,276, incorporated herein by reference, though the invention has numerous other applications.
Vent silencers are used to silence high velocity air or gas, including steam, flowing to and from the atmosphere, while also finding use in reducing discharge noises on air cylinders, vent lines, air motors, and the like.
One common form of vent silencer is the splitter type in which a perforated, rounded-nose bullet or splitter is mounted within the silencer housing and contains sound absorbing material. Sound energy passes through the holes or perforations and is absorbed in the material within the splitter.
A second common type of vent silencer is the tube-type in which a series of parallel perforated tubes are mounted within the housing and a sound absorbing material is packed around the tubes. The tube-type silencer acts to enhance the effectiveness of the sound absorbing material by providing an increased ratio of perimeter to flow passage cross sectional area.
A critical parameter in tube-type vent silencers is the length to diameter ratio of the tube. The silencer is typically rated or graded according to such ratio. For example a grade 10 silencer has a length to diameter ratio of the tube of 10. A grade 20 silencer has a length to diameter ratio of 20. A grade 30 silencer has a length to diameter ratio of 30. The grade level is a measure of acoustical silencing or damping. To accommodate a desired amount of exhaust gas or air flow through the silencer, a given total cross sectional area of the tubes is required, which in turn determines the number and/or diameter of the tubes, which further in turn determines the length of the tubes, to achieve a desired rating or grade.
In the past, the tubes have been welded to the divider walls in the housing. This is a costly and highly labor-intensive operation. Furthermore, this requires a trade-off in selecting the number of tubes versus the diameter of the tubes. It is desirable to have as many tubes as possible for a given cross sectional area flow requirement because the smaller the diameter of the tube the lesser the length of the tube required to maintain the requisite length to diameter ratio. The shorter tube lengths also provide a lower weight and shorter overall structure which is more desirable in various applications. However, the higher the number of tubes, the more welding operations required, which in turn increases cost. In order to keep cost down, including welding cost, it is typical to employ a small number of large diameter tubes. The trade-off is the longer length of tube required to maintain the requisite length to diameter ratio, which increased length adds weight and requires more axial space.
The present invention addresses and solves the above noted problems, and provides simplified cost-effective structure enabling a high number of small diameter short length tubes without the above noted cost trade-off. The invention also enables maximum use of the cross sectional area within the housing by enabling selection of the proper number of tubes to fill a circular housing in the most space-efficient pattern.